This paper presents a category of detection schemes for Multiple-Input Multiple-Output (MIMO) system called Parallel Sphere Decoder (PSD). Compared to the conventional depth-first sphere decoder with Schnorr-Euchner enumeration (SE-SD), the proposed PSD algorithms use parallel computations and achieve approximately 50% searching time reductions under the same amount of computations. Namely, in hardware implementation, the proposed work provides trade-off between computational time and computing units. Simulations of the proposed algorithms in 4×4 16-QAM and 3×3 64-QAM MIMO systems show the searching time reductions of the proposed algorithms while maintaining ML performances.